1. Field of the Invention
The invention relates to a cylinder lock, more particularly to a dual backset deadbolt assembly for a cylinder lock.
2. Description of the Related Art
Referring to FIG. 1, a deadbolt assembly 7 is installed operatively within a deadbolt hole 91 formed in one edge of a door panel 9. Screws 75 are used to mount a face plate 72 of the deadbolt assembly 7 on the door panel 9. A lock body 8 is installed in a lock hole 92 formed in the door panel 9 and transverse to the axis of the deadbolt hole 91. The lock body 8 has a deadbolt operating spindle 81 and a pair of internally threaded hollow fasteners 82 which extend respectively through a drive unit 74 and a pair of fastener holes 73 of the deadbolt assembly 7. When the lock body 8 is rotated, the spindle 81 rotates so as to actuate the driving unit of the deadbolt assembly 7, thereby retracting the deadbolt 71 into the deadbolt housing 76.
The distance between the edge of the door panel 9 and the axis of the lock hole 92 is known as the backset. Presently, there are two commonly used standard backset lengths, namely 23/8 inches (60 mm) and 23/4 inches (70 mm). Deadbolt assemblies which are adjustable between the two standard backset lengths have been disclosed in U.S. Pat. Nos. 4,615,549, 4,750,766, 5,074,605, 5,102,175 and Re.34,240. The conventional deadbolt assemblies, however, are inconvenient to install. For example, U.S. Pat. No. Re.34,240 discloses a deadbolt assembly with spaced first and second pairs of engagement members formed on one side of a transmission plate thereof. A cam drive unit of the deadbolt assembly is movable between a longer backset position, wherein the cam drive unit is rotatable so as to engage the first pair of engagement members, and a shorter backset position, wherein the cam drive unit is rotatable so as to engage the second pair of engagement members. It is noted that a slight rotation of the cam drive unit when moved from the longer backset position to the shorter backset position can result in untimely engagement between the cam drive unit and the first pair of engagement members, thereby preventing adjustment of the backset length of the deadbolt assembly to result in inconvenience during installation.